This invention pertains to tourniquets for facilitating surgical procedures performed on upper and lower limbs. Surgical tourniquets are generally employed to establish a bloodless operative field in a limb distal to an encircling cuff by regulating a pressure applied to the limb by the cuff near a pressure sufficient to stop arterial blood flow past the cuff during the surgical procedure. Surgical tourniquets of the prior art typically include an inflatable cuff for encircling a limb, an automatic pressure regulator for inflating the cuff to maintain a pressure applied by the cuff to the limb near a reference pressure selected by an operator or determined automatically, an elapsed time indicator to indicate the duration of application of pressure to the limb and an operator interface to facilitate operator control and interaction. A typical pneumatic tourniquet of the prior art is disclosed by McEwen in U.S. Pat. No. 4,469,099.
A "physiologic tourniquet" is generally considered to be a tourniquet which has the capability of maintaining the pressure applied by the cuff to the limb near the minimum pressure required to stop the flow of arterial blood past the cuff during the surgical procedure. This minimum pressure is affected by variables related to the physiology of the surgical patient, the type of surgical procedure to be performed and its likely duration, the type of cuff employed and its location and snugness on the limb, the technique employed by the surgeon and the anesthetist, and other factors. Tourniquet apparatus useful in automatically estimating and employing such a minimum pressure is disclosed by McEwen in U.S. Pat. No. 4,479,494, in U.S. Pat. No. 4,770,175 and in a pending U.S. Divisional patent application having Ser. No. 08/128,478 filed on Sep. 28, 1993.
Surgical tourniquets are typically employed as follows. A suitable inflatable cuff is first selected by an operator and applied snugly to the limb on which surgery is to be performed so that the cuff is located between the heart and the operative site on the limb. Considerations involving the design, selection and application of cuffs have been described by McEwen, for example in U.S. Pat. No. 4,605,010, in U.S. Pat. No. 5,181,522 and in U.S. Pat. No. 5,312,431. After application of a suitable cuff, the portion of the limb distal to the cuff is then exsanguinated, often by wrapping the limb with an elastic bandage, beginning at the end of the limb and wrapping tightly towards the heart up to the cuff location. While the limb is thus exsanguinated, the tourniquet instrument is typically used to inflate the cuff and maintain it at a predetermined cuff pressure sufficient to stop the inflow of arterial blood past the cuff. The elastic bandage is then removed and surgery proceeds. The pressure applied by the cuff may be changed periodically or continuously during the surgical procedure in an effort to maintain a bloodless surgical site while employing the minimum cuff pressure required to do so, as explained more fully below. Upon completion of the surgical procedure, the cuff is depressurized and removed from the patient, allowing arterial blood to flow freely into the limb.
During certain surgical procedures performed under intravenous regional anesthesia (IVRA), the surgical tourniquet system serves an additional role of preventing liquid anesthetic agent introduced into the veins in the limb distal to the cuff from flowing proximally past the cuff and out of the limb into the circulatory system. For surgical procedures where IVRA is to be employed, special cuffs having dual bladders of narrower widths are often used for encircling the limb, resulting in a first bladder encircling the limb above a second bladder which also encircles the same limb distal to the first bladder. Alternatively, two separate single-bladder cuffs of greater widths can be applied to the same limb. To maintain the pressures applied by one dual-bladder cuff or two single-bladder cuffs near selected reference pressures, one tourniquet instrument having a dual-channel automatic pressure regulator may be employed, or two separate tourniquet instruments, each having one automatic pressure regulator, may be employed. Prior art tourniquet apparatus for intravenous regional anesthesia is described by McEwen in U.S. Pat. No. 5,254,087.
Before the commencement of a surgical procedure, an operator typically configures a pneumatic tourniquet of the prior art as follows. Upon the initial supply of electrical power to a tourniquet of the prior art having one or two pneumatic channels, the levels of cuff reference pressures and time limits for elapsed time indicators and alarms are automatically set to standard, arbitrary default levels set by the manufacturer. The operator may then employ controls and displays forming part of the operator interface to change the configuration of the cuff reference pressures and the time limits to levels appropriate for the patient's physiology, the type of surgical procedure to be performed and its probable duration, the type of cuff employed and its snugness of application, and the technique to be employed by the surgeon and anesthetist. Often such changes to the configuration are not made, because an operator does not have sufficient time available to do so, or because an operator has not been trained in how to make the changes, or because an operator has not been trained concerning what levels to set on the basis of the variables listed above. If such changes to the configuration are not made by an operator, then the performance of the tourniquet will be sub-optimal. Excessively high or low reference pressures will result in either a higher probability of nerve injury in the limb encircled by the cuff or leakage of blood and in some cases liquid anesthetic agent. Also, a sub-optimal time limit either will result in a significant reduction or elimination of the utility of warning the surgeon of an excessive period of cuff pressurization for a particular procedure surgical value of elapsed time alarms in reducing tourniquet time if the time limit setting is excessively high, or will result in an annoyance and distraction to surgical and anesthesia staff if the time limit setting is too low.
Even if an electrically powered pneumatic tourniquet of the prior art has been configured by an operator to have levels of reference pressures and time limits which are more appropriate than the arbitrary default levels set when electrical power is first supplied, such configured levels are not retained upon the inadvertent or intentional interruption of electrical power to such prior art tourniquets. Upon the resumption of electrical power to such prior art tourniquets, the reference pressures and time limits are again set to the same arbitrary and sub-optimal default levels.
The applicant is unaware of any electrically powered surgical tourniquet in the prior art having the capability of optimizing, customizing, simplifying, and reducing the time required for, the configuration of the tourniquet on the basis of patient physiology, type of surgical procedure, type of cuff employed and operator technique, so that parameters such as the reference pressure levels and the levels of elapsed time limits can be set to near-optimum levels either automatically or by an operator, retained during an inadvertent or intentional interruption of electrical power to the tourniquet, and reproduced as the initial configuration parameter levels upon a resumption of the supply of electrical power to the tourniquet.
Regardless of how parameters such as the reference pressures and time limits are initially configured in a surgical tourniquet, a large number of different events occurring during a surgical procedure and associated with tourniquet usage affect patient safety, the quality of the bloodless surgical field distal to the tourniquet cuff, and longer-term patient outcomes. For example, as mentioned above, it is recognized that the level, distribution, and duration of pressure applied by the cuff to the limb will affect the nature and extent of injuries associated with tourniquet usage. It is now generally known that every usage of a surgical tourniquet results in some patient injury, and it is thought that the nature and extent of such injury can be minimized by improved setting, regulation and monitoring of the level, distribution and duration of the pressure applied by the tourniquet, by promptly identifying and responding to potentially hazardous events involving tourniquet usage, and by post-operatively relating incidents, hazards and undesirable outcomes such as nerve damage or paralysis, muscle weakness and soft tissue damage to pertinent intra-operative events associated with tourniquet usage.
These events associated with the use of a tourniquet include: each change in the level of the reference pressure employed by the pressure regulator of a tourniquet over the duration of tourniquet usage; any significant differences between the pressure applied by the cuff and the reference pressure; any applied pressures which exceed, or which are less than, predetermined upper or lower pressure limits respectively; and the application of pressure for a time period greater than a predetermined limit. Events may be further defined to include the level of the reference pressure or the level of the actual pressure applied by the cuff at periodic intervals throughout tourniquet usage, so that the quality of the bloodless surgical field and any hazards, injuries and undesirable patient outcomes can be related to the complete pressure-time set of events. In surgical procedures where IVRA is employed, additional events occur which are associated with tourniquet usage and which affect patient safety, the quality of the intravenous regional anesthesia, and patient outcomes. These IVRA-related events include the sequence, timing and duration of pressurization and depressurization of the bladders of a dual-bladder cuff or dual cuffs at various times during the surgical procedure, for reasons specifically related to the IVRA technique.
Typically in the prior art, some of such predetermined events are noted by surgical or anesthesia staff and are recorded manually in surgical or anesthesia records. For example, many operators record total tourniquet time and the initial reference pressure level. However, such manual recording of events is incomplete and inconsistent within institutions, among institutions, and even among individuals in the same operating room. Also, the recording of significant events may be delayed or not be done at all, as the surgical staff may be attending to the patient as a result of the occurrence of such significant events.
The applicant is not aware of any electrically powered tourniquet having the capability of registering the occurrence during limb surgery of any one of a number of such predetermined events concerning the application of pressure to the limb for occluding blood flow and maintaining IVRA, so that the registered events are retained during an inadvertent or intentional interruption of electrical power to the tourniquet, and so that the registered events can be displayed for an operator or reproduced on demand, after the restoration of electrical power.
In the prior art, some electrically powered tourniquets have employed pressure regulators which incorporate electro-pneumatic valves. Some of these prior-art tourniquets, such as the ATS 1500 Automatic Tourniquet System manufactured by Zimmer Inc. of Dover Ohio, use one valve for inflation and one valve for deflation of each cuff and incorporate a safety circuit for detecting and responding safely to a limited range of abnormal and hazardous actuations of the valves. However, the applicant is not aware of any tourniquet in the prior art which has multiple inflation valves and multiple deflation valves and which also has a safety circuit for detecting and responding safely to a wide range of valve related hazards including certain non-actuations of the valves, failure of one of the multiple inflation or deflation valves, or abnormal or undesired actuations of combinations of valves.